Integrated circuits, the key components in thousands of electronic and computer products, are interconnected networks of electrical components fabricated on a common foundation, or substrate. Fabricators generally build these circuits layer by layer, using techniques, such as deposition, doping, masking, and etching, to form thousands and even millions of microscopic resistors, transistors, and other electrical components on a silicon substrate, known as a wafer. The components are then wired, or interconnected, together to define a specific electric circuit, such as a computer memory.
One common technique for forming layers in an integrated circuit is called chemical vapor deposition. Chemical vapor deposition generally entails placing a substrate in a reaction chamber, heating the substrate to prescribed temperatures, and introducing one or more gases, known as precursor gases, into the chamber to begin a deposition cycle. The precursor gases enter the chamber through a gas-distribution fixture, such as a gas ring or a showerhead, one or more centimeters above the substrate, and descend toward the heated substrate. The gases react with each other and/or the heated substrate, blanketing its surface with a layer of material. An exhaust system then pumps gaseous by-products or leftovers from the reaction out of the chamber through a separate outlet to complete the deposition cycle.
Conventional chemical-vapor-deposition (CVD) systems suffer from at least two problems. First, conventional CVD systems generally form layers that include microscopic hills and valleys and thus have non-uniform thickness. In the past, fabricators have been able to overcome these hills and valleys through use of post-deposition planarization or other compensation techniques. However, escalating demands for greater circuit density, for thinner layers, and for larger substrates make it increasingly difficult, if not completely impractical, to overcome the non-uniform thickness of conventional CVD layers.
Second, some conventional CVD systems are also inefficient and time consuming. One significant factor affecting both CVD efficiency and duration is the size of conventional reaction chambers, which are generally made large to allow a loading mechanism to insert and extract the substrate. Large chambers generally require more gases to be introduced to achieve desired gas concentrations. However, much of this gas is not only unnecessary based on the amount of material deposited, but is typically treated as waste. Moreover, large chambers also take longer to fill up or pump out, prolonging deposition cycles and thus slowing fabrication of integrated circuits.
Accordingly, there is a need for better systems and methods of chemical-vapor deposition.